Polyurethane-based friable sealing compound

ABSTRACT

A polyurethane friable sealing compound free of solvent and plasticizer having a shore A hardness of below 40 and consisting essentially of a polyol component and an isocyanate component. The polyol component is selected from modified triglycerides obtained by partial ring opening of epoxidized triglycerides of a fatty acid mixture containing olefinically unsaturated fatty acids and monohydric or polyhydric alcohols. The isocyanate component is selected from polyfunctional aromatic and aliphatic isocyanates, wherein the OH:NCO equivalent ratio is from 1:0.1 to 1:1.15.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a polyurethane-based friable sealing compoundproduced from a polyol component and an isocyanate component.

In many fields of industry, a housing, a tube or similar articles haveto be sealed at their open end(s) so that moisture or water is unable topenetrate. This applies in particular to cables for the transmission ofinformation, for example in the communications field and in variousparts of the electrical industry.

2. Discussion of Related Art

Communications cables consist of a plurality of electrically conductivewires which are bunched together, several such bunches being,accommodated in an outer protective sheath. To join two such cables oreven to join cables of different construction to one another, thesebunches of wires have tn be fanned out and joined to the wires of theother cable. The individual wires thus joined have to be insulated fromone another, so that, in some cases, a much more bulky structure isformed. Since the insulation of the individual wires was opened, thisstructure has to be protected against the penetration of moisture orwater. This is done by so-called cable fittings in the form ofconnectors consisting of a joint box and a plastics materialaccommodated therein, this plastics material being known as a friablesealing compound because it is required to show high notch sensitivity.Friable sealing compounds can be removed easily by hand without any needfor special tools. They must have a high volume resistance, for examplewhere they are used in cable fittings, and in addition their so-calledpot life during processing should be long but, if necessary, should beable to be shortened by addition of catalysts.

In view of the efforts being made to replace petrochemical products byrenewable raw materials, it would be desirable if friable sealingcompounds could be provided on the same basis. Finally, a friablesealing compound should as far as possible be a homogeneous product,i.e. a uniform product with no additives.

DESCRIPTION OF THE INVENTION

The problem of providing such friable sealing compounds pounds has beensolved by the friable sealing compound according to claim 1. Furtheradvantageous embodiment can be found in the subsidiary claims.

Accordingly, the friable sealing compounds according to the inventionconsist of only one technical product of which the polyol component isobtained from renewable raw materials. They have high stability instorage and a high electrical resistance coupled with excellentfriability. In addition, they are free both from solvents and fromplasticizers so that there is no separation or migration of suchadditives with the disadvantages normally involved. In addition, thefriable sealing compounds according to the invention are, surprisingly,completely transparent which enables electrical connections etc.embedded in the friable sealing compound according to the invention tobe visually and hence non-destructively inspected so that faults in needof repair can be located much more easily and unnecessary work andwastage of material can be avoided.

The polyol component according to the invention is selected frommodified triglycerides, for example of the type described in DE-A1 32 46612, which can be obtained by partial ring opening of epoxidizedtriglycerides of a fatty acid mixture at least partly containingolefinically unsaturated fatty acids with monohydric or polyhydricalcohols.

In principle, the isocyanate component according to the invention may beselected from any of the usual poly-functional aromatic and aliphaticisocyanates, such as for example even oligomeric or polymeric isocyanatecompounds, of which HDI trimer (tris-6-isocyanatohexyl isocyanurate),polyisocyanate (4,4-diphenylmethane diisocyanate (MDI)) and HDI biuret(1,3,5-tri-(6-isocyanatohexyl)-biuret are mentioned as examples.Non-toxic compounds which do not require identification are particularlypreferred.

The OH:NCO equivalent ratio is 1:0.1 to 1:1.15 and, more particularly,1:0.4 to 1:1.25.

The friable sealing compounds according to the invention have volumeresistances of 10¹⁰ ohm×cm and higher. The volume resistances aredetermined in accordance with DIN 53482/VDI 0303, Part 3.

The hardness of the polyurethane-based friable sealing compoundsaccording to the invention may if necessary be varied within wide limitsthrough the epoxide value or the OH value of the ring-opened epoxidizedtriglyceride. Thus, a polyol component having a high epoxide value and acorrespondingly low OH value leads to relatively soft friable sealingcompounds while a polyol component having a low epoxide value and acorrespondingly high OH value leads to relatively hard, i.e. highlycrosslinked, friable sealing compounds.

The polyols suitable for use in accordance with the invention areprepared as follows:

EXAMPLE 1: PREPARATION OF POLYOL I

28.2 kg methanol and 0. 444 kg sulfuric acid were introduced into astirred tank reactor and heated with stirring to approx. 50° C. 103.8 kgsoybean oil epoxide (Ep. 0=6.8% ) were then added and the temperaturewas slowly increased to the reflux temperature of the methanol (approx.65° C). After the addition, the epoxide value of the reaction mixturewas monitored during the further course of the reaction. At an Ep. 0value of 2.6% in the reaction mixture, the catalyst sulfuric acid wasneutralized by addition of approx. 0.444 kg diethyl ethanolamine (pHcontrol, pH=8-9) and the excess methanol was distilled off in vacuo.Approx. 110 kg of a clear yellow liquid are thus obtained (residualepoxide content 3.0%).

EXAMPLE 2: PREPARATION OF POLYOL II

3530 g soybean oil epoxide were reacted with 960 g methanol as inExample 1. At an epoxide value of 3.9% Ep. 0 in the reaction mixture,the catalyst sulfuric acid was neutralized with diethyl ethanolamine andthe excess methanol was distilled off. The product (3600 g) is a yellowclear liquid (residual epoxide content 4.5%).

EXAMPLE 3: PREPARATION OF POLYOL III

400 kg soybean oil epoxide were reacted with 110 kg methanol as inExample 1. At an epoxide value of 4.4% Ep. 0 in the reaction mixture,the catalyst sulfuric acid was neutralized with diethyl ethanolamine andthe excess methanol was distilled off. The product (406 kg) is a yellowclear liquid (residual epoxide content 5.3%).

Particulars of the production and properties of the completelytransparent friable sealing compounds according to the invention areshown in Tables 1a and 1b below:

                  TABLE 1a                                                        ______________________________________                                        Isocyanate: HDI Trimer (NCO: 22%)                                             Tris-(6-isocyanatohexyl isocyanurate)                                         Example  1         2         3       4                                        ______________________________________                                        Polyol   Polyol 3  Polyol 2  Polyol 1                                                                              Polyol 1                                 OH value Approx. 50                                                                              Approx. 70                                                                              Approx. Approx.                                                               105     105                                      % Ep. O  5.3       4.5       3.0     3.0                                      Equimolar                                                                              1:1       1:1       1:1     1:0.5                                    OH:NCO                                                                        ratios                                                                        Polyol:  100:17    100:24    100:34  100:17                                   isocyanate                                                                    (parts by wt.)                                                                Pot life.sup.1)                                                                        Approx.   Approx. 90                                                                              Approx. 90                                                                            Approx. 90                               (mins.)  120                                                                  Shore A                                                                       hardness                                                                      After 1 d                                                                              5, Friable                                                                              21, Friable                                                                             45, Non-                                                                              14, Friable                                                           friable                                          After 14 d                                                                             15, Friable                                                                             35, Friable                                                                             60, Non-                                                                              20, Friable                                                           friable                                          ______________________________________                                         .sup.1) Room temperature with addition of 0.1% Formrez U1 24 (a Witco         product)                                                                 

                  TABLE 1b                                                        ______________________________________                                        Isocyanate: MDI Polymer (NCO 30%)                                             Example    5          6          7                                            ______________________________________                                        Polyol     Polyol 3   Polyol 2   Polyol 1                                     OH value   Approx. 50 Approx. 70 Approx. 105                                  % Ep. O    5.3        4.5        3.0                                          Equimolar  1:0.74     1:0.73     1:0.74                                       OH:NCO                                                                        ratios                                                                        Polyol:    100:12.5   100:17.5   100:26                                       isocyanate                                                                    (parts by wt.)                                                                Pot life.sup.1)                                                                          Approx. 90 Approx. 60 Approx. 30                                   (mins.)                                                                       Shore A hardness                                                              After 1 d  5, Friable 5, Friable 45, Non-friable                              After 14 d 15, Friable                                                                              25, Friable                                                                              65, Non-friable                              ______________________________________                                         .sup.1) Room temperature with addition of 0.1% Formrez U1 24 (a Witco         product)                                                                 

It can be seen from Tables la and lb that Examples 3 and 7 relate tocompounds which are not suitable as friable sealing compounds accordingto the invention, as reflected in the shore A hardness values. It maygenerally be assumed that compounds having a Shore A hardness of about40 or higher lead to unsatisfactory products.

Tables 2 and 3 below provide further particulars of the startingmaterials and properties of the compounds obtained. The polyols listedin Table 2 are soya polyols containing approx. 3%, 4.5% and 5.3% epoxideoxygen according to DE-A1 33 46 612. These soya polyols were cast withisocyanate in various equimolar OH:NCO ratios and the electrical volumeresistances were measured.

In the event of undercrosslinking with isocyanate, there was adeterioration in the electrical properties and an increase in thetackiness of the compound obtained.

It can be seen from Table 3 that friability, good electrical propertiesand minimal tackiness were obtained using the soya polyol polyol 3 (OHvalue 50/epoxide oxygen 5.3%) and the soya polyol polyol 2 (OH value70/epoxide oxygen 4.7%) after equimolar crosslinking with an HDI trimer.

Hardening of the compounds obtained was accelerated by addition of thecatalyst Formrez UL 24.

The addition of soybean oil epoxide (Edenol D 81, a product of HenkelKGaA) to polyol 1 led to exudation of the plasticizer after casting withthe HDI trimer, so that the product obtained was unsatisfactory.

                  TABLE 2                                                         ______________________________________                                        Raw material specifications                                                   ______________________________________                                        Polyols OH Value    OH Equivalent                                                                              % Fr. epoxide                                ______________________________________                                        Polyol 1                                                                              Approx. 100 561          Approx. 3                                    Polyol 2                                                                              Approx. 70  800          Approx. 4.7                                  Polyol 3                                                                              Approx. 50  1122         Approx. 5.3                                  ______________________________________                                        Isocyanate   % NCO    NCO Equivalent                                          ______________________________________                                        HDI trimer   22       191                                                     22% NCO                                                                       ______________________________________                                        Catalyst    Formrez UL 24 (organotin compound)                                            (Witco)                                                           Formulation:                                                                            100.0  parts polyol                                                           0.1    part Formrez UL 24                                                     X      parts HDI trimer (dependent upon the                                          OH value of the polyol)                                      ______________________________________                                    

                                      TABLE 3                                     __________________________________________________________________________    Properties                                                                    Mixing ratio                                                                              Equimolar                                                         OH:NCO      OH:NCO                                                                              Volume resis-                                               (parts by wt.)                                                                            ratio tivity (Ω · Ohm)                                                        Remarks                                            __________________________________________________________________________    Polyol 1                                                                           100:18 1:0.53                                                                              5.0 · 10.sup.10                                                               47% undercrosslinked                                                          readily friable, slightly tacky                         100:15 1:0.44                                                                              3.5 · 10.sup.10                                                               56% undercrosslinked                                                          friable, very tacky                                100:12      1:0.35                                                                              Cannot be measured - material too tacky                     Polyol 2                                                                           100:24 1:1   1.09 · 10.sup.11                                                              100% crosslinked,                                                             barely tacky, readily friable                           100:20 1:0.83                                                                              7.5 · 10.sup.10                                                               17% undercrosslinked                                                          slightly tacky, readily friable                         100:16 1:0.67                                                                              2.7 · 10.sup.10                                                               34% undercrosslinked,                                                         very tacky, readily friable                        Polyol 3                                                                           100:17 1:1   1.6 · 10.sup.10                                                               100% crosslinked, slightly tacky                                              highly friable                                          100:15 1:0.88                                                                              1.4 · 10.sup.10                                                               12% undercrosslinked,                                                         very tacky, readily friable                             100:13 1:0.76                                                                              1.3 · 10.sup.10                                                               24% undercrosslinked,                                                         extremely tacky, friable                           __________________________________________________________________________     Hardener: HDI trimer, 22% NCO                                            

We claim:
 1. A polyurethane friable sealing compound free of solvent andplasticizer, said sealing compound consisting essentially of a polyolcomponent and an isocyanate component, said polyol component beingselected from the group consisting of modified triglycerides obtained bypartial ring opening of epoxidized triglycerides of a fatty acid mixturecontaining olefinically unsaturated fatty acids with monohydric orpolyhydric alcohols, said isocyanate component being selected from thegroup consisting of polyfunctional aromatic and aliphatic isocyanates,wherein the OH:NCO equivalent ratio is from 1:0.1 to 1:1.5 and the OHvalue of the polyol, and the OH:NCO ratio of said friable sealingcompound result in said friable sealing compound having a Shore Ahardness value of less than about
 40. 2. A sealing compound as in claim1 having a volume resistance of at least 10¹⁰ ohm×cm as determined inaccordance with
 3. A sealing compound as in claim 1 wherein saidisocyanate component is selected from the group consisting oftris-6isocyanatohexyl isocyanurate, 4,4-diphenylmethane diisocyanate,and 1,3,5-tri-(6-isocyanatohexyl)-biuret.